It's Not Easy Keeping Greens

To keep collard greens as fresh as possible, one trick is to fresh-cut the bases of the stems as if they were cut flowers, and then keep them in a cool place in a bowl of cold water. This trick will work on many of the fibrous vegetables with strong “veins” that draw water up into their leaves and florets. Other examples include broccoli. As for the radishes, twist the leaves off when you get them home. Otherwise, the water in the root or radish bulb travels up into the leaf as it ordinarily would, and is wicked away through evaporation - but not replaced, as the radish obviously is no longer in the earth.